It is desirable that the transfer of light between the optical fibers of mated optical fiber connectors be accomplished with a minimum loss of signal; i.e., with low insertion loss. Insertion loss may result from several factors, including the presence of a gap or separation between the ends of the connected fibers. Specifically, some light is lost if the end faces of two fibers are separated because light diverges as it radiates from the end of a fiber. In addition, fiber to fiber separation results in an insertion loss due to Fresnel reflections at the two glass-air interfaces between the spaced fibers. Accordingly, it is important that end faces of connected fibers be maintained in virtual contact with one another to minimize these losses.
Contact between the fibers of mated connectors is improved by polishing the fiber end faces. Typically, the end face of a fiber is polished by mounting a connector with protruding fiber to a polishing tool. The tool is then moved over a polishing medium by hand until the end face of the fiber is satisfactorily polished.
U.S. Pat. No. 5,018,316 discloses a polishing fixture particularly designed for polishing the end face of an optical fiber carried within a ceramic alignment ferrule of an optical fiber connector of the push-pull plug assembly type such as bayonet connector assembly. The polishing fixture of the patent comprises a body member having a front disk-shaped surface with a web of gutters formed therein. A profiled bore extends through the body member and is adapted to receive the front end of the ferrule having the optical fiber therein such that the end face of the ferrule extends slightly beyond the front surface of the polishing fixture. The fixture further includes means for attaching the fixture to an optical fiber connector of the push-pull plug assembly type.
As described in the patent, to polish the optical fiber of the connector, the fixture having the optical fiber connector attached thereto is grasped by hand and placed against a polishing medium. The end faces of the ferrule and of the optical fiber carried therein are then polished by moving the fixture in a figure eight pattern over the polishing medium. After polishing, the ceramic tip and fiber optic end face are observed under a microscope. An acceptable polished face will show fine polishing scratches, without any large pits although small peripheral chips may be permissible. If large chips appear in the center of the fiber, this means that further polishing is required or that the end face is unacceptable and the fiber must be re-terminated and repolished.
FIGS. 9 and 10 illustrate a known polishing bushing particularly designed for polishing the end face of an optical fiber carried in an alignment ferrule of an optical fiber connector of the bayonet lock type. The polishing bushing, which is generally designated by reference number 10, comprises a body portion 12 defining a disk-shaped front surface 13 having a web of gutters 14 formed therein. A central profiled bore 16 extends through the body portion 12 and is adapted to receive the end of an alignment ferrule carrying an optical fiber to be polished. The bushing further includes means 17 for securing the optical fiber connector to the bushing which comprises an annular alignment sleeve 18 extending rearwardly from the back face of the body portion 12. As shown in FIG. 10, a pair of diametrically opposed latching lugs 19 extend inwardly from the inner surface of the sleeve 18 for latching a bayonet lock type connector to the fixture.
In operation of the fixture of FIGS. 9 and 10, a bayonet lock type connector is inserted into the alignment sleeve and latched in place by the latching lugs such that the end of the alignment ferrule thereof and the optical fiber carried thereby extends through profiled bore 16 and protrudes slightly beyond the front surface 13 of the bushing. The bushing is then pressed lightly against the surface of a polishing medium and moved thereover by hand as described above until polishing is completed.
Although the polishing fixtures described in U.S. Pat. No. 5,018,316 and illustrated in FIGS. 9 and 10 of the present application are effective in polishing the end faces of optical fibers in a controlled, reliable manner; there is a need for a polishing bushing which will provide an operator with greater sensitivity of feel during the polishing operation and an ability to more closely monitor the polishing operation while it is being performed without removing the bushing from the polishing medium. It is also desirable to provide a polishing bushing that is light in weight, comfortable to hold and use and which provides a greater polishing speed.